In a pump example described in document FR 2 885 890, the pump comprises a resilient diaphragm having a portion that forms a check valve so as to prevent the fluid returning from the metering chamber back into the reservoir. The resilient diaphragm is fitted on a support through which a feed channel passes, the support serving as a seat for the portion that forms the check valve so that the valve is pressed against the seat to block the liquid, or is spaced apart from the seat so as to allow it to pass. The diaphragm is slidably mounted in the metering chamber of the pump in leaktight manner in order to expel out from the chamber any fluid contained in the chamber. More precisely, the resilient diaphragm comprises a transverse wall forming the valve for closing the chamber feed channel, and a cylindrical skirt having one or two peripheral sealing lips in sliding contact with the inner wall of the metering chamber.
It is also known that certain pumps are configured to deliver fluid without intake of air, thereby making it possible in particular to avoid using preservatives. In such devices in particular, any introduction of air into the pump or the reservoir is to the detriment of the accuracy with which doses are delivered and to the sterility of the fluid that is delivered.